This application relates generally to unmixed fuel processors and methods for using the same.
With its abundant domestic supply, coal is one of the most secure, reliable, and affordable energy supplies for the U.S. today, gasification of coal to produce electricity is being commercially introduced as Integrated Gasification Combined Cycle (IGCC) power plants. However, one of the major problems in modern industrial society is air pollution by conventional combustion systems based on biomass and fossil fuels. The oldest recognized air pollution problem is the emission of smoke. In modern boilers and furnaces, smoke emissions could be eliminated or at least greatly reduced by the use of Over Fire Air (“OFA”) technology. Other types of air pollution produced by combustion include particulate emissions such as fine particles of ash from pulverized coal firing, oxides of sulfur (SO2 and SO3), carbon monoxide emissions, volatile hydrocarbon emissions and the release of two oxides of nitrogen, NO and NO2. More recently, the problem of global warming due to greenhouse gas emissions of CO2 from power plants and other combustion systems have become a matter of serious environmental concern.
Another major technological problem concerns the use of coal as a fuel for powering gas turbines. Gas turbines are the lowest capital cost systems available for generating electrical power. Since the thermodynamic efficiency of gas turbines increases with increasing turbine inlet temperature, efforts to improve turbine efficiency generally involve increasing the turbine inlet temperature to higher levels. As a result, turbine blades and other components have been engineered to tolerate increasing high inlet temperatures. It is well known that the hot gases produced by coal firing contain fly ash (which is erosive to turbine blades). In the presence of this erosive fly ash the maximum service temperature at which turbine blades can operate is less than it would be otherwise. This limitation significantly decreases the overall process efficiency and lowers the competitiveness of coal as a gas turbine fuel. These and other disadvantages have also prevented lower cost (and abundant) coal from being considered an attractive gas turbine fuel. If a process were developed whereby coal could be burned in a manner that produced hot gases that were not erosive or corrosive, the need for temperature reduction would be eliminated and coal would become a much more economically viable gas turbine fuel.
U.S. Pat. Nos. 5,339,754, 5,509,362, and 5,827,496, disclose a method of burning fuels using a catalyst that is readily reduced when in an oxidized state and readily oxidized when in a reduced state, with the fuel and air being alternatively contacted with the catalyst. The fuel reduces the catalyst and is oxidized to carbon dioxide (CO2) and water vapor. In turn, the air oxidizes the catalyst and becomes depleted of oxygen. Combustion can thereby be effected without the need of mixing the fuel and air prior to, or during, the combustion process. If means are provided whereby the CO2 and water vapor and the oxygen depleted air can be directed in different directions as they leave the combustion process, the mixing of fuel and air can be completely avoided. This particular method of combustion has become known in the art as “unmixed combustion”.
One of the major challenges with unmixed combustion types of technologies is the handling of ash in the solid carbonaceous fuel. The alkali metal oxides in the ash can melt under the operating conditions and can create agglomerates with the other solids present in the reactor. This may result into huge loss of reliability/availability of such type of technologies. Hence, there continues to be a need for unmixed combustion technologies that address the agglomeration issue.